Other Comprehensive Income - Schedule of Accumulated Other Comprehensive Income, Net of Tax (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			$ (1,119,219)
Other comprehensive income (loss), net of tax	$ (33,061)	$ (162,889)	(190,125)	$ 43,267
Ending Balance	(1,309,344)		(1,309,344)
Securities Available For Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			(1,094,794)	(1,313,791)
Other comprehensive income (loss) before reclassifications			(190,786)	41,936
Reclassification of amounts included in net income			0	(43)
Other comprehensive income (loss), net of tax			(190,786)	41,893
Ending Balance	(1,285,580)	(1,271,898)	(1,285,580)	(1,271,898)
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			(24,425)	(34,503)
Other comprehensive income (loss) before reclassifications			0	0
Reclassification of amounts included in net income			661	1,374
Other comprehensive income (loss), net of tax			661	1,374
Ending Balance	(23,764)	(33,129)	(23,764)	(33,129)
AOCI Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			(1,119,219)	(1,348,294)
Other comprehensive income (loss) before reclassifications			(190,786)	41,936
Reclassification of amounts included in net income			661	1,331
Other comprehensive income (loss), net of tax			(190,125)	43,267
Ending Balance	$ (1,309,344)	$ (1,305,027)	$ (1,309,344)	$ (1,305,027)